docs: def render_asides(self, block, view_name, frag, context):
          """
          Collect all of the asides' add ons and format them into the frag. The frag already
          has the given block's rendering.
          """
          aside_frag_fns = []
          for aside in self.get_asides(block):
              aside_view_fn = aside.aside_view_declaration(view_name)
              if aside_view_fn is not None:
                  aside_frag_fns.append((aside, aside_view_fn))
          if aside_frag_fns:
              # layout (overideable by other runtimes)
              return self.layout_asides(block, context, frag, view_name, aside_frag_fns)
          return frag